Hi neon; In order for someone to help you it really would help if we had some more information. Graphics card and model number of the Pavillion for instance.
Look in Device Manager under Disply Adapters for info about your card.
Right click My Computer. Click properties. Click Device Manager. Click the + by Display Adapters. Also while you are there do you see a yellow ? or ! by i?
You may also want to see if there are any driver updates for it on the HP site.
http://welcome.hp.com/country/us/en/support.html
As for the model number of your Pavillion try holding down the Ctrl and Alt keys then press S on your keyboard. Otherwise look for a nameplate on the front or a sticker on the side or a label on the back.
As for the system requirements for Portal for anyone who wants to know these are what's listed at the site;
Minimum: 1.7 GHz Processor, 512MB RAM, DirectX 8 level Graphics Card, Windows Vista/XP/2000, Mouse, Keyboard, Internet Connection
Recommended: Pentium 4 processor (3.0GHz, or better), 1GB RAM, DirectX 9 level Graphics Card, Windows Vista/XP/2000, Mouse, Keyboard, Internet Connection
neon if you could find out what Norton product you have please do. Two antivirus programs can cause trouble;
RandyL